Cryptographic Hash Functions and Their Uses BDC Practice Questions (Page 4)

Questions 16–20

1. 16foundation · easy

   Why does changing even a single bit in a message produce a completely different hash value?

   • ABecause the hash function encrypts the data with a key
   • BBecause the hash function uses a random seed that changes each time
   • CBecause of the avalanche effect, a small change in input results in a significantly different output
   • DBecause the hash function compresses the data, losing information
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2. 17expert · hard

   A blockchain developer is designing a new proof-of-work algorithm. They want to make mining resistant to ASIC specialization. Which approach is most aligned with using hash functions to achieve this goal?

   • AUse a hash function with a shorter output length to reduce computational work.
   • BUse a memory-hard hash function that requires significant memory to compute.
   • CUse a simple hash like SHA-256 with a higher difficulty target.
   • DUse a hash function that is deterministic and fast.
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4. 18application · medium

   A developer is implementing a digital signature scheme for a document management system. The system must sign large PDF files efficiently. The developer decides to hash the document before signing. Which property of the hash function makes this approach secure?

   • APreimage resistance ensures that the original document cannot be recovered from the hash.
   • BThe avalanche effect guarantees that changing one bit in the document changes the signature completely, making forgery detectable.
   • CDeterminism ensures that the same document always produces the same hash, so the signature can be verified offline.
   • DCollision resistance ensures that an attacker cannot find two different documents that produce the same hash, so a valid signature on one cannot be transferred to another.
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5. 19application · medium

   A blockchain protocol uses a Merkle tree to commit to a large set of transactions. A light client wants to verify that a specific transaction is included in a block. Which data must the client obtain from a full node to perform this verification?

   • AThe Merkle root and the digital signature of the block producer.
   • BThe entire list of transactions in the block and the Merkle root.
   • CThe transaction itself and the sibling hashes along the path from the transaction's leaf to the Merkle root.
   • DThe block header and the transaction's index in the block.
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6. 20expert · hard

   A company is migrating from a legacy system that stores passwords as unsalted MD5 hashes. They want to upgrade without forcing all users to reset passwords immediately. Which approach is the most secure and practical?

   • AImmediately rehash all existing MD5 hashes with Argon2id.
   • BOn next successful login, rehash the password with Argon2id and a new random salt, then update the stored record.
   • CKeep MD5 hashes but add a global salt to all of them.
   • DStore both the MD5 hash and the Argon2id hash for each user.
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